Autonomous vehicles are a rapidly growing area of research and development. While current publicity generally involves the autonomous passenger automobile, the applications for autonomous vehicles are wide ranging. One exemplary application of particular interest is agricultural implements.
Regardless of the application, the central feature of autonomous vehicles is the manner in which it senses its environment and navigates without human input. In a general sense, autonomous vehicle guidance involves guiding the vehicle along a planned vehicle trajectory path. The planned vehicle trajectory path often is represented as a curve. In a simplest form of a guidance system, the curve can be reduced to a piecewise linear curve that connects reference points or waypoints with linear segments, as illustrated generally in FIG. 1A. The piecewise linear curve suffers from several deficiencies. For example, at each reference point, the vehicle is required to instantaneously change its heading, which is not feasible while maintaining a desired speed. The abrupt change in the radius of curvature of the path results in the vehicle overshooting the subsequent linear segment and deviating from the path. Therefore, a need exists in the art for an improved system and method for representing the planned vehicle trajectory as a curve so as to avoid inducing unpleasant discontinuities and errors.
One such system and method includes defining the position, tangent direction and instantaneous curvature of the curve. U.S. Pat. No. 8,131,415 to Peake, which is herein incorporated by reference in its entirety, discloses providing a smooth curve representation of the planned trajectory by interpolating between adjacent waypoints with cubic splines. The interpolation method produces smooth curves to compute the instantaneous curvature of the guidance curve, which in turn is used to compute a steer angle and guide the vehicle.
While an improvement over piecewise linear curves, curve representation through interpolation can undesirably result in chaotic oversteering in response to the introduction of external errors. For example, as the vehicle rolls back and forth over uneven terrain during recording of reference points, side-to-side roll error in the reference point locations can create exaggerated instantaneous curvature in the trajectory path. Since, by its mathematical nature, interpolation requires the curve representation to pass precisely through each reference point, the control system, in response to the exaggerated instantaneous curvature, can command a steer angle that chaotically swings the steered wheels from side to side to attempt to correct the vehicle's path. The result is not only undesirable, but also can cause further guidance error. Therefore, a need exists in the art for an improved guidance system and method that attenuates problematic determinations of exaggerated instantaneous curvature and prevents induction of spurious steer angles.